1. Technical Field
The present invention relates to a vehicle-mounted power supply system including a first secondary battery, a second secondary battery, and a rotary machine having a power generation function for charging the first and second batteries.
2. Related Art
A known vehicle-mounted power supply system, as disclosed in Japanese Patent Application Laid-Open Publication No. 2012-80706, selectively uses a lead battery (as a first secondary battery) and a lithium-ion battery (as a second secondary battery) to supply power to various vehicle-mounted electrical loads. More specifically, the system electrically connects the lithium-ion battery to an alternator and the lead battery through a semiconductor switch.
During a regeneration period, placing the semiconductor switch in an on state allows for power supply from the alternator to the lithium-ion battery. During a non-regeneration period, placing the semiconductor switch in an off state allows for power supply from the lithium-ion battery to an electrical load disposed on the lithium-ion battery side of the semiconductor switch. Controlling the semiconductor switch in such a manner can lead to efficient use of the regenerated power.
In recent years, a rotary machine is available that includes a power generation function for generating electrical power by receiving a torque from an output shaft of an internal-combustion engine of the vehicle, a start-up function for starting the internal-combustion engine by applying an initial rotation to the output shaft of the internal-combustion engine of the vehicle, and an output assist function for assisting the output of the internal-combustion engine by applying a torque to the output shaft of the internal-combustion engine of the vehicle.
It can be considered that the rotary machine configured as above having the power generation function, the start-up function, and the output assist function is used in the vehicle-mounted power supply system in place of a conventional alternator. In such a configuration, the rotary machine is powered by the secondary batteries to drive the output shaft of the engine of the vehicle during the start-up and during the output assist. However, more power is consumed in the rotary machine than in the electrical loads (other than the rotary machine) connected to the secondary batteries. Accordingly, during the start-up and during the output assist, a higher current flows through the secondary batteries that supply power to the rotary machine, which may cause output voltage drops of the secondary batteries. The output voltage drops of the secondary batteries may lead to destabilized operations of the electrical loads (other than the rotary machine) powered by the secondary batteries.
In consideration of the foregoing, it would therefore be desirable to have a vehicle-mounted power supply system including a first secondary battery, a second secondary battery, and a connection switch for connecting and disconnecting the first and second secondary batteries, capable of advantageously executing power supply to an electrical load on the second secondary battery side of the connection switch connected between the first and second secondary batteries.